This invention generally relates to power supplies. More particularly, this invention relates to inverter power supplies employed in welding, cutting and heating applications.
Power supplies typically convert a power input to a necessary or desirable power output tailored for a specific application. In welding applications, power supplies typically receive a high voltage alternating current (VAC) signal and provide a high current output welding signal. For example, welding power supplies can receive an input such as 208 VAC single-phase, 208 VAC three-phase, 230 VAC single phase, 230 VAC three-phase, 460 VAC single-phase, or 460 VAC three-phase low current power to produce an approximately 10-40 VDC high current welding output.
Generally, a welding power supply is designed for a specific power input. In other words, the power supply cannot provide essentially the same output over the various input power levels. Further, components which operate safely at a particular input power level are often damaged when operating at an alternative input power level. Therefore, power supplies in the prior art have provided for these various inputs by employing circuits which can be manually adjusted to accommodate a variety of inputs. These circuits generally may be adjusted by changing the transformer turns ratio, changing the impedance of particular circuits in the power supply or arranging tank circuits to be in series or in parallel. In these prior art devices, the operator was required to identify the voltage of the input and then manually adjust the circuit for the particular input.
Generally, adapting to the various voltage inputs in the prior art requires that the power supply be opened and cables be adjusted to accommodate the particular voltage input. Thus, the operator was required to manually link the power supply so that the appropriate output voltage was generated. Operating an improperly linked power supply could result in personal injury, power supply failure or insufficient power.
Prior art devices accommodated this problem by configuring the power supply to operate at two different VAC input levels. For example, U.S. Pat. No. 4,845,607, issued to Nakao et al. on Jul. 4, 1989, discloses a power source which is equipped with voltage doubling circuits that are automatically activated when the input is on the order of 115 VAC, and which is deactivated when the input is on the order of 230 VAC. Such sources are designed to operate at the higher voltage level, with the voltage doubling circuit providing the required voltage when the input voltage is at the lower level. This type of source, which uses a voltage doubling circuit, must use transistors or switching devices as well as other components capable of withstanding impractical high power levels to implement the voltage doubling circuit. Further, the circuitry associated with the voltage doubling circuit inherently involves heat dissipation problems. Also, the voltage doubling circuit type of power supply is not fully effective for use in welding applications. Thus, there is a long felt need for a power supply for use in welding applications which can automatically be configured for various VAC input levels.
Welding power supplies are generally known which receive a high VAC signal and generate a high current DC signal. A particularly effective type of the power source for welding applications which avoids certain disadvantages of the voltage doubling circuit type of power supply generally relies on a high frequency power inverter. Inverter power sources convert high voltage DC power into high voltage AC power. The AC power is provided to a transformer which produces a high current output. High frequency power inverters include semiconductor components which are susceptible to breakdown and poor performance over input voltage ranges.
Power inverters for use over input voltage ranges are generally known in the art. For example, a power inverter which is capable of using two input voltage levels is disclosed in U.S. Pat. No. 3,815,009, issued to Berger on Jun. 4, 1974. The power inverter of that patent utilizes two switching circuits; the two switching circuits are connected serially when connected to the higher input voltage, but are connected in parallel to account for the lower input voltage. The switching circuits are coupled to each other by means of lead wires. This inverter is susceptible to operator errors in configuring the switching circuits for the appropriate voltage level, which can result in power source malfunction or human injury. Thus, there is a need for an inverter power supply which can be automatically configured for various voltage inputs.